Printhead nozzle arrangement employing variable volume nozzle chamber

ABSTRACT

A printhead has a plurality of nozzle arrangements. Each nozzle arrangement includes an ink inlet aperture for receiving ink into the nozzle arrangmenet; a wall portion bounding the ink inlet aperture; a crown portion arranged opposite the ink inlet aperture and defining a nozzle opening; a skirt portion depending from the crown portion to form part of a peripheral wall of the nozzle arrangement, the crown and skirt portions being displaceable with respect to the wall portion towards the substrate to alter a volume of a nozzle chamber defined by the wall, crown and skirt portions; and a thermal actuator interconnecting the crown portion with the substrate, the actuator for displacing the crown and skirt portions. The wall portion is angled inwardly with respect to the nozzle chamber defined by the wall, crown, and skirt portions. The wall portion defines a lip at a to free end thereof, the lip for facilitating the formation of a fluidic seal with the skirt portion.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/688,893 filed Jan. 17, 2010, which is a Continuation of U.S.application Ser. No. 12/324,806 filed on Nov. 26, 2008, now issued U.S.Pat. No. 7,654,644, which is a Continuation Application of U.S.application Ser. No. 11/967,235 filed on Dec. 30, 2007, now issued U.S.Pat. No. 7,465,028, which is a Continuation Application of U.S.application Ser. No. 11/209,709 filed on Aug. 24, 2005, now issued U.S.Pat. No. 7,328,971, which is a Continuation Application of U.S.application Ser. No. 10/302,276 filed on Nov. 23, 2002, now issued U.S.Pat. No. 6,966,111, which is a Continuation Application of U.S.application Ser. No. 10/183,711 filed on Jun. 28, 2002, now issued U.S.Pat. No. 6,502,306, which is a Continuation Application of U.S.application Ser. No. 09/575,125 filed on May 23, 2000, now issued U.S.Pat. No. 6,526,658, all of which are herein incorporated by reference.

Various methods, systems and apparatus relating to the present inventionare disclosed in the following co-pending applications filed by theapplicant or assignee of the present invention simultaneously with theparent application Ser. No. 11/967,235:

6,428,133 6,526,658 6,315,399 6,338,548 6,540,319 6,328,431 6,328,4256,991,320 6,383,833 6,464,332 6,390,591 7,018,016 6,328,417 6,322,1946,382,779 6,629,745 7,721,948 7,079,712 6,825,945 7,330,974 6,813,0396,987,506 7,038,797 6,980,318 6,816,274 7,102,772 7,350,236 6,681,0456,728,000 7,173,722 7,088,459 7,707,082 7,068,382 7,062,651 6,789,1946,789,191 6,644,642 6,502,614 6,622,999 6,669,385 6,549,935 6,987,5736,727,996 6,591,884 6,439,706 6,760,119 7,295,332 6,290,349 6,428,1556,785,016 6,870,966 6,822,639 6,737,591 7,055,739 7,233,320 6,830,1966,832,717 6,957,768 7,456,820 7,170,499 7,106,888 7,123,239 6,409,3236,281,912 6,604,810 6,318,920 6,488,422 6,795,215 7,154,638 6,924,9076,712,452 6,416,160 6,238,043 6,958,826 6,812,972 6,553,459 6,967,7416,956,669 6,903,766 6,804,026 7,259,889 6,975,429

These applications are incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a micro-electromechanical fluid ejectiondevice. It also relates to a method of fabricating amicro-electromechanical systems device.

BACKGROUND TO THE INVENTION As set out in the material incorporated byreference, the Applicant has developed ink jet printheads that can spana print medium and incorporate up to 84 000 nozzle assemblies.

These printheads include a number of printhead chips. One of these isthe subject of this invention. The printhead chips includemicro-electromechanical components that physically act on ink to ejectink from the printhead chips.

The printhead chips are manufactured using integrated circuitfabrication techniques. Those skilled in the art know that suchtechniques involve deposition and etching processes. The processes arecarried out until the desired integrated circuit is formed.

The micro-electromechanical components are by definition microscopic. Itfollows that integrated circuit fabrication techniques are particularlysuited to the manufacture of such components. In particular, thetechniques involve the use of sacrificial layers. The sacrificial layerssupport active layers. The active layers are shaped into components. Thesacrificial layers are etched away to free the components.

Applicant has devised a new process for such manufacture whereby twolayers of organic sacrificial material can be used to support two layersof conductive material.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, a printhead has aplurality of nozzle arrangements, and each nozzle arrangement comprises:an ink inlet aperture for receiving ink into the nozzle arrangmenet; awall portion bounding the ink inlet aperture; a crown portion arrangedopposite the ink inlet aperture and defining a nozzle opening; a skirtportion depending from the crown portion to form part of a peripheralwall of the nozzle arrangement, the crown and skirt portions beingdisplaceable with respect to the wall portion towards the substrate toalter a volume of a nozzle chamber defined by the wall, crown and skirtportions; and a thermal actuator interconnecting the crown portion withthe substrate, the actuator for displacing the crown and skirt portions.The wall portion is angled inwardly with respect to the nozzle chamberdefined by the wall, crown, and skirt portions. The wall portion definesa lip at a free end thereof, the lip for facilitating the formation of afluidic seal with the skirt portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying m diagrammatic drawings in which:

FIG. 1 shows a three dimensional, schematic view of a nozzle assembly ofa printhead chip fabricated in accordance with a method of theinvention.

FIGS. 2 to 4 show a three dimensional, schematic illustration of anoperation of a nozzle assembly of the printhead chip of FIG. 1.

FIG. 5 shows a three-dimensional view of an array of the nozzleassemblies of FIGS. 2 to 4 constituting the printhead chip of theinvention.

FIG. 6 shows, on an enlarged scale, part of the array of FIG. 5.

FIG. 7 shows a three dimensional view of the ink jet printhead chip witha nozzle guard positioned over the printhead chip.

FIGS. 8A to 8R show three-dimensional views of steps in a method, of theinvention, of fabricating a printhead chip, with reference to the nozzleassembly of FIG. 1.

FIGS. 9A to 9R show sectional side views of the steps of FIGS. 8A to 8R.

FIGS. 10A to 10K show masks used in the steps of FIGS. 8A to 8R.

FIGS. 11A to 11C show three-dimensional views of an operation of thenozzle assembly of FIG. 1.

FIGS. 12A to 12C show sectional side views of an operation of the nozzleassembly of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1 of the drawings, a nozzle assembly of a printhead chip 14(FIGS. 5 and 6) of the invention is designated generally by reference10. The printhead chip 14 has a plurality of nozzle assemblies 10arranged in an array on a wafer substrate in the form of a siliconsubstrate 16. The substrate 16 incorporates a drive circuitry layer inthe form of a CMOS layer.

A dielectric layer 18 is deposited on the substrate 16. A CMOSpassivation layer 20 is deposited on the dielectric layer 18 to protectthe drive circuitry layer.

Each nozzle assembly 10 includes nozzle chamber walls 22 defining an inkejection port 24 in a roof wall 30 and a nozzle chamber 34. The inkejection port 24 is in fluid communication with the nozzle chamber 34. Alever arm 26 extends from the roof wall 30. An actuator 28 is anchoredto the substrate 16 at one end and is connected to the lever arm 26 atan opposite end.

The roof wall is in the form of a crown portion 30. A skirt portion 32depends from the crown portion 30. The skirt portion 32 forms a firstpart of a peripheral wall of the nozzle chamber 34.

The crown portion 30 defines a raised rim 36, which “pins” a meniscus 38(FIG. 2) of a body of ink 40 in the nozzle chamber 34.

An ink inlet in the form of an aperture 42 (shown most clearly in FIG. 6of the drawings) is defined in a floor 46 of the nozzle chamber 34. Theaperture 42 is in fluid communication with an ink inlet channel 48defined through the substrate 16.

A second part of the peripheral wall in the form of a wall portion 50bounds the aperture 42 and extends upwardly from the floor 46.

The wall portion 50 has an inwardly directed lip 52 at its free end,which serves as a fluidic seal. The fluidic seal inhibits the escape ofink when the crown and skirt portions 30, 32 are displaced, as describedin greater detail below.

It will be appreciated that, due to the viscosity of the ink 40 and thesmall dimensions of the spacing between the lip 52 and the skirt portion32, the inwardly directed lip 52 and surface tension function as a sealfor inhibiting the escape of ink from the nozzle chamber 34.

The actuator 28 is a thermal bend actuator and is connected to an anchor54 extending upwardly from the substrate 16 or, more particularly, fromthe CMOS passivation layer 20. The anchor 54 is mounted on conductivepads 56 which form an electrical connection with the actuator 28.

The actuator 28 comprises a first, active beam 58 arranged above asecond, passive beam 60. In a preferred embodiment, both beams 58 and 60are of, or include, a conductive ceramic material such as titaniumnitride (TiN).

Both beams 58 and 60 have their first ends anchored to the anchor 54 andtheir opposed ends connected to the arm 26. When a current is caused toflow through the active beam 58 thermal expansion of the beam 58results. As the passive beam 60, through which there is no current flow,does not expand at the same rate, a bending moment is created causingthe arm 26 and thus the crown and skirt portions 30, 32 to be displaceddownwardly towards the substrate 16 as shown in FIG. 3 of the drawings.This causes an ejection of ink through the ink ejection port 24 as shownat 62 in FIG. 3 of the drawings. When the source of heat is removed fromthe active beam 58, i.e. by stopping current flow, the portions 30, 32return to a quiescent position as shown in FIG. 4 of the drawings. Thereturn movement causes an ink droplet 64 to form as a result of thebreaking of an ink droplet neck as illustrated at 66 in FIG. 4 of thedrawings. The ink droplet 64 then travels on to the print media such asa sheet of paper. As a result of the formation of the ink droplet 64, a“negative” meniscus is formed as shown at 68 in FIG. 4 of the drawings.This “negative” meniscus 68 results in an inflow of ink 40 into thenozzle chamber 34 such that a new meniscus 38 (FIG. 2) is formed inreadiness for the next ink drop ejection from the nozzle assembly 10.

The nozzle array 14 is described in greater detail in FIGS. 5 and 6. Thearray 14 is for a four-color printhead. Accordingly, the array 14includes four groups 70 of nozzle assemblies, one for each color. Eachgroup 70 has its nozzle assemblies 10 arranged in two rows 72 and 74.One of the groups 70 is shown in greater detail in FIG. 6 of thedrawings.

To facilitate close packing of the nozzle assemblies 10 in the rows 72and 74, the nozzle assemblies 10 in the row 74 are offset or staggeredwith respect to the nozzle assemblies 10 in the row 72. Also, the nozzleassemblies 10 in the row 72 are spaced apart sufficiently far from eachother to enable the lever arms 26 of the nozzle assemblies 10 in the row74 to pass between adjacent nozzle chamber walls 22 of the assemblies 10in the row 72. It is to be noted that each nozzle assembly 10 issubstantially dumbbell shaped so that the nozzle chamber walls 22 in therow 72 nest between the nozzle chamber walls 22 and the actuators 28 ofadjacent nozzle assemblies 10 in the row 74.

Further, to facilitate close packing of the nozzle chamber walls 22 inthe rows 72 and 74, the nozzle chamber walls 22 are substantiallyhexagonally shaped.

It will be appreciated by those skilled in the art that, when the crownand skirt portions 30, 32 are displaced towards the substrate 16, inuse, due to the ink ejection port 24 being at a slight angle withrespect to the nozzle chamber 34, ink is ejected slightly off theperpendicular. It is an advantage of the arrangement shown in FIGS. 5and 6 of the drawings that the actuators 28 of the nozzle assemblies 10in the rows 72 and 74 extend in the same direction to one side of therows 72 and 74. Hence, the ink droplets ejected from the ink ejectionports 24 in the row 72 and the ink droplets ejected from the inkejection ports 24 in the row 74 are parallel to one another resulting inan improved print quality.

Also, as shown in FIG. 5 of the drawings, the substrate 16 has bond pads76 arranged thereon which provide the electrical connections, via thepads 56, to the actuators 28 of the nozzle assemblies 10. Theseelectrical connections are formed via the CMOS layer (not shown).

Referring to FIG. 7 of the drawings, a development of the invention isshown. With reference to the previous drawings, like reference numeralsrefer to like parts, unless otherwise specified.

A nozzle guard 80 is mounted on the substrate 16 of the array 14. Thenozzle guard 80 includes a planar cover member 82 that defines aplurality of passages 84. The passages 84 are in register with thenozzle openings 24 of the nozzle assemblies 10 of the array 14 suchthat, when ink is ejected from any one of the nozzle openings 24, theink passes through the associated passage 84 before striking the printmedia.

The cover member 82 is mounted in spaced relationship relative to thenozzle assemblies 10 by a support structure in the form of limbs orstruts 86. One of the struts 86 has air inlet openings 88 definedtherein.

The cover member 82 and the struts 86 are of a wafer substrate. Thus,the passages 84 are formed with a suitable etching process carried outon the cover member 82. The cover member 82 has a thickness of not morethan approximately 300 microns. This speeds the etching process. Thus,the manufacturing cost is minimized by reducing etch time.

In use, when the printhead chip 14 is in operation, air is chargedthrough the inlet openings 88 to be forced through the passages 84together with ink travelling through the passages 84.

The ink is not entrained in the air since the air is charged through thepassages 84 at a different velocity from that of the ink droplets 64.For example, the ink droplets 64 are ejected from the ink ejection ports24 at a velocity of approximately 3 m/s. The air is charged through thepassages 84 at a velocity of approximately 1 m/s.

The purpose of the air is to maintain the passages 84 clear of foreignparticles. A danger exists that these foreign particles, such as dustparticles, could fall onto the nozzle assemblies 10 adversely affectingtheir operation. With the provision of the air inlet openings 88 in thenozzle guard 80 this problem is, to a large extent, obviated.

Referring now to FIGS. 8 to 10 of the drawings, a process formanufacturing the printhead chip 14 is described with reference to oneof the nozzle assemblies 10.

Starting with the silicon substrate or wafer 16, the dielectric layer 18is deposited on a surface of the wafer 16. The dielectric layer 18 is inthe form of approximately 1.5 microns of CVD oxide. Resist is spun on tothe layer 18 and the layer 18 is exposed to mask 100 and is subsequentlydeveloped.

After being developed, the layer 18 is plasma etched down to the siliconlayer 16. The resist is then stripped and the layer 18 is cleaned. Thisstep defines the ink inlet aperture 42.

In FIG. 8 b of the drawings, approximately 0.8 microns of aluminum 102is deposited on the layer 18. Resist is spun on and the aluminum 102 isexposed to mask 104 and developed. The aluminum 102 is plasma etcheddown to the dielectric layer 18, the resist is stripped and the deviceis cleaned. This step provides the bond pads 56 and interconnects to theink jet actuator 28. This interconnect is to an NMOS drive transistorand a power plane with connections made in the CMOS layer (not shown).

Approximately 0.5 microns of PECVD nitride is deposited as the CMOSpassivation layer 20. Resist is spun on and the layer 20 is exposed tomask 106 whereafter it is developed. After development, the nitride isplasma etched down to the aluminum layer 102 and the silicon layer 16 inthe region of the inlet aperture 42. The resist is stripped and thedevice cleaned.

A layer 108 of a sacrificial material is spun on to the layer 20. Thelayer 108 is 6 microns of photosensitive polyimide or approximately 4microns of high temperature resist. The layer 108 is softbaked and isthen exposed to mask 110 whereafter it is developed. The layer 108 isthen hardbaked at 400° C. for one hour where the layer 108 is comprisedof polyimide or at greater than 300° C. where the layer 108 is hightemperature resist. It is to be noted in the drawings that thepattern-dependent distortion of the polyimide layer 108 caused byshrinkage is taken into account in the design of the mask 110.

In the next step, shown in FIG. 8 e of the drawings, a secondsacrificial layer 112 is applied. The layer 112 is either 2 microns ofphotosensitive polyimide, which is spun on, or approximately 1.3 micronsof high temperature resist. The layer 112 is softbaked and exposed tomask 114. After exposure to the mask 114, the layer 112 is developed. Inthe case of the layer 112 being polyimide, the layer 112 is hardbaked at400° C. for approximately one hour. Where the layer 112 is resist, it ishardbaked at greater than 300° C. for approximately one hour.

A 0.2-micron multi-layer metal layer 116 is then deposited. Part of thislayer 116 forms the passive beam 60 of the actuator 28.

The layer 116 is formed by sputtering 1,000 angstroms of titaniumnitride (TiN) at around 300° C. followed by sputtering 50 angstroms oftantalum nitride (TaN). A further 1,000 angstroms of TiN is sputtered onfollowed by 50 angstroms of TaN and a further 1,000 angstroms of TiN.

Other materials, which can be used instead of TiN, are TiB₂, MoSi₂ or(Ti, Al)N.

The layer 116 is then exposed to mask 118, developed and plasma etcheddown to the layer 112 whereafter resist, applied to the layer 116, iswet stripped taking care not to remove the cured layers 108 or 112.

A third sacrificial layer 120 is applied by spinning on 4 microns ofphotosensitive polyimide or approximately 2.6 microns high temperatureresist. The layer 120 is softbaked whereafter it is exposed to mask 122.The exposed layer is then developed followed by hardbaking. In the caseof polyimide, the layer 120 is hardbaked at 400° C. for approximatelyone hour or at greater than 300° C. where the layer 120 comprisesresist.

A second multi-layer metal layer 124 is applied to the layer 120. Theconstituents of the layer 124 are the same as the layer 116 and areapplied in the same manner It will be appreciated that both layers 116and 124 are electrically conductive layers.

The layer 124 is exposed to mask 126 and is then developed. The layer124 is plasma etched down to the polyimide or resist layer 120whereafter resist applied for the layer 124 is wet stripped taking carenot to remove the cured layers 108, 112 or 120. It will be noted thatthe remaining part of the layer 124 defines the active beam 58 of theactuator 28.

A fourth sacrificial layer 128 is applied by spinning on 4 μm ofphotosensitive polyimide or approximately 2.6 μm of high temperatureresist. The layer 128 is softbaked, exposed to the mask 130 and is thendeveloped to leave the island portions as shown in FIG. 9 k of thedrawings. The remaining portions of the layer 128 are hardbaked at 400°C. for approximately one hour in the case of polyimide or at greaterthan 300° C. for resist.

As shown in FIG. 81 of the drawing a high Young's modulus dielectriclayer 132 is deposited. The layer 132 is constituted by approximately 1micron of silicon nitride or aluminum oxide. The layer 132 is depositedat a temperature below the hardbaked temperature of the sacrificiallayers 108, 112, 120, 128. The primary characteristics required for thisdielectric layer 132 are a high elastic modulus, chemical inertness andgood adhesion to TiN.

A fifth sacrificial layer 134 is applied by spinning on 2 microns ofphotosensitive polyimide or approximately 1.3 microns of hightemperature resist. The layer 134 is softbaked, exposed to mask 136 anddeveloped. The remaining portion of the layer 134 is then hardbaked at400° C. for one hour in the case of the polyimide or at greater than300° C. for the resist.

The dielectric layer 132 is plasma etched down to the sacrificial layer128 taking care not to remove any of the sacrificial layer 134.

This step defines the nozzle opening 24, the lever arm 26 and the anchor54 of the nozzle assembly 10.

A high Young's modulus dielectric layer 138 is deposited. This layer 138is formed by depositing 0.2 micron of silicon nitride or aluminumnitride at a temperature below the hardbaked temperature of thesacrificial layers 108, 112, 120 and 128.

Then, as shown in FIG. 8 p of the drawings, the layer 138 isanisotropically plasma etched to a depth of 0.35 microns. This etch isintended to clear the dielectric from the entire surface except thesidewalls of the dielectric layer 132 and the sacrificial layer 134.This step creates the nozzle rim 36 around the nozzle opening 24, which“pins” the meniscus 38 of ink, as described above.

An ultraviolet (UV) release tape 140 is applied. 4 Microns of resist isspun on to a rear of the silicon wafer 16. The wafer 16 is exposed to amask 142 to back etch the wafer 16 to define the ink inlet channel 48.The resist is then stripped from the wafer 16.

A further UV release tape (not shown) is applied to a rear of the wafer16 and the tape 140 is removed. The sacrificial layers 108, 112, 120,128 and 134 are stripped in oxygen plasma to provide the final nozzleassembly 10 as shown in FIGS. 8R and 9R of the drawings. For ease ofreference, the reference numerals illustrated in these two drawings arethe same as those in FIG. 1 of the drawings to indicate the relevantparts of the nozzle assembly 10. FIGS. 11 and 12 show the operation ofthe nozzle assembly 10, manufactured in accordance with the processdescribed above with reference to FIGS. 8 and 9, and these figurescorrespond to FIGS. 2 to 4 of the drawings.

As is clear from the drawings and the description, the layer 116 formsthe wall portion 50 as well as the passive beam 60 of the actuator 28.It follows that the steps of depositing the layer 116 and etching thelayer 116 results in the fabrication of two components of each nozzleassembly.

As discussed in the background, the saving of a step or steps in thefabrication of a chip can result in the saving of substantial expensesin mass manufacture. It follows that the fact that the wall portion 50can be fabricated in a common stage with the passive beam 60 of theactuator 28 saves a substantial amount of cost and time.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive. I/We claim:

1. A printhead having a plurality of nozzle arrangements, each nozzlearrangement comprising: an ink inlet aperture for receiving ink into thenozzle arrangmenet; a wall portion bounding the ink inlet aperture; acrown portion arranged opposite the ink inlet aperture and defining anozzle opening; a skirt portion depending from the crown portion to formpart of a peripheral wall of the nozzle arrangement, the crown and skirtportions being displaceable with respect to the wall portion towards thesubstrate to alter a volume of a nozzle chamber defined by the wall,crown and skirt portions; and a thermal actuator interconnecting thecrown portion with the substrate, the actuator for displacing the crownand skirt portions, wherein the wall portion is angled inwardly withrespect to the nozzle chamber defined by the wall, crown, and skirtportions, and the wall portion defines a lip at a free end thereof, thelip for facilitating the formation of a fluidic seal with the skirtportion.
 2. The printhead of claim 1, wherein each nozzle arrangementfurther comprises a layer of micro-electromechanical drive circuitry foractuating the actuator.
 3. The printhead of claim 1, wherein theactuator has a first active beam arranged above a second passive beam,the beams fabricated from a conductive ceramic material with anelectrical connection between the active beam and the drive circuitryestablished via conductive pads.
 4. The printhead of claim 1, whereinthe skirt portion defines a first part of a peripheral wall of thenozzle chamber and the wall portion defines a second part of theperipheral wall of the nozzle chamber.
 5. The printhead of claim 1,wherein the actuator is connected to an anchor extending upwardly from asubstrate in which the ink inlet aperture is defined, said anchormounted on the conductive pads to form an electrical connection with theactuator.
 6. The printhead of claim 1, wherein the nozzle opening isarranged at an angle to the vertical so that ejection of ink deviatesfrom the perpendicular.
 7. The printhead of claim 1, further comprisinga nozzle guard having a planar cover member positioned on a supportstructure extending from the substrate, the planar cover member defininga plurality of passages, each passage being in register with arespective nozzle opening.
 8. The printhead of claim 7, wherein thesupport structure of the nozzle guard defines a number of openings forpermitting the ingress of air into a region between the printhead andthe cover member, whereby air is permitted to pass through the passages.